Interpretive Summary: The objective of the present study was to determine if injections of ghrelin, a hormone known to stimulate hunger and feeding in rats, mice, and humans, would increase feed intake, weight gain, and alter hormonal profiles in pigs during the period immediately following weaning. We conducted an experiment with 24 pigs receiving one of two treatments. The ghrelin injection treatment group included pigs that received intravenous injections of ghrelin for five days. The control pigs received saline and were treated similarly. Pig weights and feed intakes were measured daily and activity observations and blood samples were taken to measure effect of ghrelin on feeding activity and various hormones in the blood. Blood samples were analyzed for ghrelin, the growth regulating hormones, and hormones that are associated with body fat, stress, and glucose usage. The data indicated that ghrelin increased weight gain in pigs during the weaning period, but had a negligible effect on feed intake. Two observation periods during the experiment showed more pigs in the ghrelin treatment eating during the observation period when compared to saline-treated pigs. Concentrations of ghrelin as well as a growth regulating hormone (growth hormone), energy usage hormone (insulin), and stress hormone (cortisol) increased following the initial ghrelin injection. These observations provide evidence that ghrelin may positively influence weight gain, while concomitantly increasing hormones that influence growth, energy usage, and stress in weaned pigs. This study demonstrated the potential of increasing feed efficiency and gain by supplementing the hormonal signals that increase appetite and control the secretion of growth hormones, stress hormones, and hormones that are important for energy utilization from the feed. The low feed intake and weight loss associated with weaning may increase the pigs susceptibility to disease. If a method of increasing feed intake and weight gain in pigs can be developed, the health and growth of the pig will be increased. This will result in pigs that reach market weight faster, thus saving the producer money associated with feed, medication, and facility costs. The end result will be an increased efficiency of pork production. This data will be of interest to all individuals associated with swine production including scientists in academia, government, and industry.

Technical Abstract:
The study objectives were to determine relative gain, feed intake, behavior, and endocrine parameters in recently weaned pigs receiving exogenous ghrelin. Twenty-four barrows were weaned at 18 d of age (d 0 of study) and were assigned to either a ghrelin injection (GR; n=12) or a saline injection group (CON; n=12). Starting on d 1, GR pigs were injected three times daily for 5 d with 2 ug/kg human ghrelin and CON pigs were similarly injected with saline. Activity observations and blood samples were taken at -15, 0, 15, 30, 60, 90, 120, 240, and 480 min relative to the first injection and then three times daily (0800, 1600, and 2400 h) for 8 d. Weight gain during the 5 d injection period was greater (P = 0.04) in the GR-treated than CON-treated pigs. The initial injection of ghrelin elevated serum concentrations of ghrelin, GH, insulin, and cortisol (P < 0.05). Serum IGF-1 initially fell in both treatment groups from d 1 to 2 (P < 0.05), but then increased from d 5 to 8 (P < 0.05). Peripheral concentrations of glucose in the GR-treated pigs were greater on d 2, 3, 7, and 8 than on d 1 (P < 0.05). For both treatment groups, peripheral concentrations of leptin increased from d 7 to 8 and cortisol decreased from d 1 to 5. These observations provide evidence that ghrelin may positively influence weight gain, while concomitantly increasing GH, insulin, and cortisol secretion in weaned pigs.